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Hardware Description
3-36
Copyright © ARM Limited 2000. All rights reserved.
3.9.4
Power sensing and management
Two of the Analog-to-Digital Converters (ADCs) within the keyboard controller are
used to sense power usage by measuring the voltage across a 0.015
Ω
shunt resistor. A
sample is taken from the source side of the shunt, and a second from the load side of the
shunt. The current through the shunt can be calculated using Ohms Law:
60 x (V
sample_source
– V
sample_load
)
The keyboard controller has four states relating to power management, as listed in Table
3-18.
CRITICAL SUSPEND
The
PSU_BATT_OK
signal from the power supply places the
keyboard into the CRITICAL SUSPEND state on a transition
from HIGH to LOW. The state disables all keys and turns off all
LEDs. It remains in this state until the
PSU_BATT_OK
signal
transitions to a HIGH. Normal state for this signal is HIGH.
LID CLOSED
This state can be entered from either the state of the physical pin
(when enabled) or under software control. The controller can be
activated as follows:
An external switch (GIO20 or GIO21 transition). If
_LID
is
HIGH, only the external switch (XSW1 or 2) activates the
keyboard controller. If the lid is open then any of the GIO
switches activate the keyboard.
ACTIVE
This state is entered when a key switch is pressed. This method is
valid only if the lid is open, the
PSU_BATT_OK
signal is asserted
and the
nWKUP
pin is not being driven from the PLD (open drain
buffer turned OFF). When the PLD shuts down the keyboard, only
the software selected wake up keys can re-activate it.
Table 3-18 Power management states
Host State
UR8HC007 Pin Name
PWROK
_LID
_HSUS
Critical Suspend (low battery)
0
x
x
Lid closed
1
1
x
SA-1100 suspended (sleep)
1
0
1
Active
1
0
0
Содержание Prospector P1100
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